Conventionally a sensor determines a specific physical quantity. For determining a phenomenon or a state, plural physical quantities are measured separately, and the measurement results are collectively analyzed. For example, a property of a material detectable by touch feeling, such as hardness and a temperature, can be sensed by use of a combination of miniaturized sensors, as described in a document: J. Engel et al., Sensors and Actuators, A117, 50 (2005).
In recording with an ink-jet printer or a copying machine, various information-recording paper sheet materials (hereinafter referred to simply as “recording sheets”). The recording sheets are viscoelastic. For image formation, physical properties or a state of the recording sheet should be detected for setting the optimum image formation conditions. The information on the recording sheet includes thickness, roughness, density, rigidity, moisture content, electric resistivity, temperature, sizing, kind of paper (paper category such as plain paper, rough paper, gloss paper, and coated paper, and paper model number), and so forth. The kind and category of the paper are not properties but a state of the recording sheet. The paper-type number is an identification number given by the paper maker. The properties and the states of the recording sheet are not uniformly reflected to image formation conditions. For example, in electrophotographic copying, for delivery of a recording sheet, paper sheet thickness, sheet rigidity, and sheet deformability are important, whereas in the processes of image development, image transfer, and image fixation, surface resistivity, moisture content, roughness, gloss, and the kind of paper are important. The methods of determination of properties and states of the paper sheet such as thickness and density are standardized by Japanese Industrial Standard (JIS), and described also in the document: “ENOMAE Toshiharu: Nippon Gazoh Gakkai-shi (Journal of Image Technology Society of Japan) vol. 43, (No. 4), 276 (2004)”.